1. Field of the Invention
The present invention relates to a rotor of a rotary electric machine, the rotor including a rotor core and a permanent magnet embedded in the rotor core.
2. Description of Related Art
In a permanent magnet synchronous rotary electric machine configured such that permanent magnets are embedded in a rotor core, when a temperature of a rotor increases along with driving of the rotary electric machine, not only magnet performance decreases to decrease torque and efficiency, but also demagnetization of the permanent magnets occurs due to high temperature. If a magnet having a high coercive force is employed, a problem with demagnetization can be avoided. However, in this case, it is necessary to increase a content of heavy rare earth, which causes an increase in cost.
In view of this, in order to cool down the rotary electric machine, various structures have been suggested conventionally. For example, Japanese Patent Application Publication No. 2008-228522 (JP 2008-228522 A) describes a technique in which oil supplied from a supply oil passage formed inside a rotating shaft is discharged through a plurality of cooling oil passages formed inside a rotor core, so as to cool down a rotor. In JP 2008-228522 A, slots extending on q-axes of the rotary electric machine are formed on each of a plurality of electromagnetic steel sheets arranged consecutively in an axial direction, such that the slots on respective electromagnetic steel sheets are formed in radial ranges shifted from each other, thereby forming the cooling oil passages extending on the q-axes.
Further, Japanese Patent Application Publication No. 2006-067777 (JP 2006-067777 A) describes a technique in which oil supplied from a supply oil passage formed inside a rotating shaft is discharged through a plurality of cooling oil passages formed inside a rotor core, so as to cool down a rotor. In JP 2006-067777 A, the cooling oil passages extend on d-axes of a rotary electric machine. In JP 2006-067777 A, the plurality of oil passages extending in a radial direction is arranged in an axial direction.